The invention relates generally to scanning documents and in particular, to apparatus for scanning selected portions of large documents.
Various systems have been used for selecting portions of a document to be scanned. According to one approach, the original document is placed on a digitizer pad where the area to be scanned is mapped by an operator using, for example, a cross-hairs device to define coordinates of selected boundaries, and the coordinates are entered into a computer through the digitizing mechanism. The document is then transferred to a scanning table, using a known registration, and the stored coordinates are recalled. As the document is scanned, only the area within the designated boundaries is recorded, while the area outside the designated boundaries is excluded.
Errors often occur in this procedure as the original document is transferred from the digitizing pad to the scanning table surface. The precise coordinates recorded from the digitizer may not precisely match the scanned area if the document has been placed out of registration on the scanning table, or if the document moves during registration or scanning, for example, because of air currents.
Additionally, since the procedure described above can be used with documents having a width of eighteen inches or more, errors are often made in mapping a selected image area, since an operator may be viewing the far side of a document from an angle as he leans over the digitizer pad. As a result, incorrect coordinates may be selected for the desired image area.
A primary object of the invention is an apparatus which ensures that the precise coordinates chosen on the digitizer pad match the scanned area of the document. Another object of the invention is an apparatus which aids the operator in accurately designating coordinates of the image area to be scanned. Further objects of the invention are a simple, accurate, and reliable scanning apparatus.